This invention is motivated by the need to model, analyze and control interactions among the administratively separated subsystems of an electrically interconnected large scale power system by more direct and simpler approaches than available at present. Understanding the dynamics of interactions among subsystems is important for a variety of reasons. The most recently emerging needs are seen through the presence of the inter-area oscillations [M. Klein, G. Rogers, P. Kundur, "A Fundamental Study of Inter-area Oscillations in Power Systems", IEEE Trans. on Power System, vol. 6, no. 3, August, 1991; NYPP-OH TSWG Report, Phase V, Planning Studies, vol I, August, 1992] and the potential to control them by implementing fast, power-electronic switched controllers. The new control hardware technology of this type is presently being developed and tested anti it is often referred to as the FACTS technology [Proceedings: FACTS Conference I: The Future of High-voltage Transmission, EPRI TR-100504, March 1992;Proceedings: FACTS Conference II, EPRI TR-101784, Dec. 1992].
Much work in studying the potential of FACTS technology for controlling the inter-area dynamics has been very specific to a chosen technology, and/or to the simulation efforts to illustrate their potential performance in surpressing a specific problem of a given system. Very little work exists at present on understanding structural relations between the inter-area dynamics and the means for controlling them. For example, within a wide variety of control technologies available it is not clear which class of devices is most efficient in controlling a particular sub-class of dynamic problems. A subproblem of controlling real power dynamics by controlling directly phase angle differences across tie-lines on which phase-shifting transmission devices are located, under the assumption that coupling with voltage changes is negligible, has barely been studied in this setting.
This invention is concerned with systematic ways of using local area measurements on a large electric power system which would provide for controlling the inter-area dynamics according to desired performance specifications.
The emphasis of the invention is on the state-space variables necessary to process the measurements in such a way that this goal is achieved. This is the first time that system-wide effects of local FACTS devices are quantified in order to guarantee the performance at the system level. Instead, in prior proposed systems the FACTS devices and their local controls are tested on a specific operating problem. The set point of a local controller is assigned using quasi-static studies of the system at a Control Center level, and its rescheduling is done open-loop. The only closed-loop control has been local in nature. This invention requires dynamic measurements of selected variables from the local area, and not only at the location at which the control apparatus is located. The technology is robust with respect to the required measurements, since they can be provided with a high accuracy and are feasible in real-time using only existing technologies.